This invention relates generally to radiographic imaging systems and more particularly to processors used in such systems.
As is known in the art, radiographic cameras such as the Anger camera disclosed in U.S. Pat. No. 3,011,057 which issued in the name of H. O. Anger on Nov. 28, 1961 and in U.S. Pat. No. 3,914,611 which issued in the name of K. J. Stout on Oct. 21, 1975 are often utilized for obtaining a radiographic image of a radioactive subject. Such a camera includes a scintillator viewed by a set of scintillator detectors or photomultiplier tubes providing signals which are combined, typically, by a resistor matrix to provide a Z axis signal which represents the energy in a radioactive event, typically the amount of energy in a gamma ray particle striking the scintillator, and X and Y position signals representing the location on the scintillator which was struck by the particle.
One problem arises from the fact that with any radioactive subject a gamma ray particle emitted within the subject may collide within such subject, scatter, and lose energy. Because the gamma ray has been deflected, but still is accepted by the collimator and detector an erroneous position signal may be generated. Because of the accompanying loss of energy in the gamma particle as a result of this collision and because there are a finite number of detectors with the result that not all the light energy is detected, and because of the detector geometry and combinational arithmetic, the camera is said to have energy aberrations. A second problem results from distortions due to the combinational arithmetic causing nonlinearities in the camera system, sometimes referred to as spatial distortion. A third problem arises from such things as nonuniform doping of the scintillator crystal and the fact that a discrete number of photodetectors are used by the camera thereby varying the density of apparent locations of the radioactive events as provided by the X and Y position signals. The nonuniformity is also a result of the nonlinearity of the camera with the result being that nonuniformity causes regions of increased or reduced radioactive event density in the image of the subject thereby appearing to the clinician viewing the image as regions of greater intensity, which may be incorrectly diagnosed as a tumor or malady.